1. Field of the Invention
The invention relates to a toilet tank valve seat structure and particularly to a valve seat that has an overflow tube with an adjustable length and a plug easy to couple.
2. Description of the Prior Art
Referring to FIG. 1, a conventional valve seat 1 of a toilet tank includes a body 10 and an overflow tube 11 located on one side of the body. The overflow tube 11 has an overflow outlet 111 at the top end to discharge excessive water through a valve opening 101 to prevent the water in the tank from spilling outside the tank. The overflow tube 11 has a strut 102 on a lower side to couple with an anchor notch 121 of a stopping cap 12. The stopping cap 12 has a seal pad 122 to cover the upper side of the valve opening 101 and is driven by a chain 13 to move about the strut 102 which serves as a fulcrum to control the water to flush from the tank into the toilet. Such a structure still has problems in practice, notably:                1. The overflow tube 11 has a fixed length and must be cut to a corresponding height according to the water level. If the length of the overflow tube is not proper, or the water level is altered, the overflow tube 11 cannot function as desired, and the valve seat has to be replaced.        2. After the stopping cap 12 has been used for a period of time, the seal pad 122 could be aged and hardened, and the sealing effect is impaired. Hence the seal pad has to be replaced periodically. Due to the strut 102 and the anchor notch 121 are coupled forcefully, removing or coupling of the two could result in breaking of the strut 102 or hurting user's hands.        